Feed preferences in juvenile
cod estimated by inert lanthanid markers –
effects of moisture content in the feed
H. Otterå, O.
Garatun-Tjeldstø,
K. Julshamn, E.
Austreng-2003
Aquaculture International, 11
(1-2): 217-224
Abstract:
There are indications that low ingestion rates of
formulated feed may limit the growth of early juvenile fish, including cod.
This has particularly been observed during the weaning period, when the fish
must change from a presumably palatable live prey to usually a dry diet. The
study of the physical properties of the diet seems to be an underestimated
area of research, compared to studies on the nutritional properties of the
diet. In this study we used lanthanide markers as a tool in estimating diet
preferences for examining the effect of dietary moisture content on
ingestion rates in juvenile cod (0.8 g). Fishmeal-based diets were produced
with five levels of water, giving diets with 35, 42, 54, 65 or 95% dry
weight. Each diet was marked with a small amount of a lanthanide or yttrium
oxide. The fish were hand fed on a mixture of these five diets. Ingestion
rates where then estimated by killing 1/2 of the fish after one day and the
rest after four days of feeding. The whole fish with gut content was
homogenized and marker content was measured by ICP-MS. The amount ingested
of each of the five diets could then be calculated from these figures.
Despite the high variation in diet selection between individuals the results
clearly indicate a higher intake of moist feed. This could be caused by a
better palatability or to a higher availability caused by a lower sinking
rate of the moist feed.
(Institute of
Marine Research, POB 1870 Nordnes, N-5817 Bergen, Norway, e-mail: haakon.otteraa@imr.no)